How do I cancel an app which I do not want any more

Follow this link

See or cancel your subscriptions

Manage your subscription to Apple Music, Apple News+, Apple Arcade, Apple TV+, Apple TV channels, or subscriptions that you signed up for inside an app

https://support.apple.com/en-us/HT202039

If you have paid for an app that you no longer require, if you go to the email confirmation that you had of the purchase, you can "Report a Problem" and then request a cancellation/refund there.